Achillea lanulosa Nutt. [ =Achillea millefolium in
the sense of some authors], common yarrow, achillée millefeuille
Perennial, spreading by seeds and shallow, horizontal
rootstocks; allogamous; stem to 2 feet (6 dm.) high; flowers
white; with the exception of dandelion, common yarrow is the
most common weed in our area; pastures, lawns, meadows,
roadsides, and waste places; native to North America. Crushed
leaves can cause an allergic reaction in some people. Dairy
products produced from cows grazing on this plant can have an
undesirable flavor.

Acroptilon repens (L.) DC. [ =Centaurea repens
L.], Russian, centaurée de Russie
Perennial, forming dense patches; plants 2 to 3 feet (6 to 9
dm.) high; flowers purple to pink early, turning straw colored
at maturity; cultivated fields, grain and alfalfa fields,
pastures and waste places; a fairly recent introduction,
probably as an impurity in Turkestan alfalfa; it has become
widespread, especially in the mid-west and near-west. There are
reports of it causing poisonings and the deaths of sheep and
horses.

Ageratina altissima (L.) King & H. Rob. [=Eupatorium rugosum Houtt.], white snakeroot, eupatoire rugueuse
A perennial herb with stems 1 to 4 ft. (30 to 120 cm) tall. It has short-stalked opposite leaves and inflorescences with 10 to 30 small heads composed entirely of white disk flowers. It is a native plant of open and shady habitats in the eastern half of our area. It is very toxic if eaten. Poisonings and deaths have occurred of cattle, horses, sheep, and goats. There are some early reports of sicknesses and deaths of pioneers who drank milk from cows that had eaten white snakeroot. There are no recent reports.

Ambrosia artemisiifola L., common ragweed, petite herbe à poux
Annual, spreading by seeds; stems erect, usually 2 to 3 feet (6
to 9 dm.) high; flowers inconspicuous, wind pollinated;
throughout our area but most common in southern Ontario, Quebec
as far as Quebec City and southward in the United States;
cultivated fields, gardens, vacant lots, and especially along
the fringes of roadsides; native to North America. Its
wind-blown pollen is the most important cause of hay fever in
eastern North America. Dairy products from cows that have grazed
this plant often have an objectionable odor and taste.

Ambrosia psilostachya DC. [ =Ambrosia coronopifolia
Torr. & A.Gray], perennial ragweed, herbe à poux vivace
Perennial with horizontal rootstocks; a smaller plant with
rougher, thicker, and less lobed leaves than common ragweed, but
otherwise similar; flowers inconspicuous, wind pollinated; most
common in the mid-west and west, but has recently spread
eastward along railroad lines; native to North America. Its
wind-blown pollen causes hay fever in humans.

Ambrosia trifida L., giant ragweed, grande herbe à poux
Annual, spreading by seeds; plants 1 to 10 feet (3 to 30 dm.)
high; most common in southwestern Quebec, southern Ontario,
southern Manitoba, and southward in the United States; flowers
inconspicuous, wind pollinated; roadsides, railway lines,
agricultural fields, and waste places; native to North America.
It is far less abundant than common ragweed and its air-born
pollen is less important as a cause of hay fever.

Arctium minus Bernh., common burdock, petite bardane
Biennial; autogamous; stems 2 to 6 feet (6 to 18 dm.) high;
flowers purple; farm yards, fencerows, roadsides, and waste
places; not in cultivated fields; throughout our range, but most
common in Eastern North America; introduced from Europe. Forms a
large rosette, in the first year, that resembles rhubarb (but is
not edible). Mature flowers form prickly burs that stick to
clothing and fur.

Artemisia absinthium L., absinth, armoise absinthe
Perennial with stems to 5 feet(15 dm) high; flowers
inconspicuous; strongly aromatic; roadsides, waste places,
farmyards, pastures ,and cropland; throughout our range but
particularly abundant in the mid-west; introduced from Europe.
Causes taint in dairy products when eaten by cattle. Absinth is
used in the preparation of some alcoholic beverages and was
formerly used for medicinal purposes. Its volatile oils are
toxic if consumed in large amounts.

Artemisia biennis Willd.- biennial wormwood, armoise bisannuelle
An annual or biennial, scentless, herb; usually with only a single stem. Stems from 1 to 3 feet (3 to 9 dm.) high. Native in the western portion of our area, but probably an introduction in the eastern part. Weedy in disturbed habitats within and outside of its native range.

Artemisia vulgaris L., mugwort, armoise vulgaire
A rhizomatous perennial herb with erect stems from 2 to 8 ft. (6 to 24 dm.) tall. Originally introduced from Europe. Fragments of mugwort rhizomes, readily able to establish new plants, are believed to be its main method of spread. In some cases, mugwort can form dense monospecific stands. Mugwort is widespread along roadsides and in waste places in the eastern half of our range. Oil extracted from its foliage has been used for a variety of purposes.

Aster novae-angliae L. [=Symphyotrichum novae-angliae (L.) G.L.Nelson], New England aster, aster de Nouvelle-AngleterreNew England aster is a perennial herb with single to multiple, densely leafy, erect stems 2 to 5 ft. (60 to 150 cm.) high, with short, thick, underground rhizomes. Flower heads are large and showy, 1.5 in. (ca.4 cm.) in diameter, with yellowish disk flowers surrounded by deep-purple, blue, rose, rarely white, ray flowers. Flowering is normally late, in September and October. It is a native of moist soils along the margins of lakes, streams, and other fresh water bodies. It is a naturalized colonizer along roadsides, railway lines, and in meadows and waste places. Its showy flowers are a colorful addition to the fall landscape. It occurs in all areas except parts of the Midwest. Numerous cultivars have been produced for use as a late-flowering ornamental.

Centaurea diffusa Lam., diffuse knapweed, centaurée diffuse
Biennial to short-lived perennial; stems 2 to 3 feet (6 to 9
dm.) high; flowers white or purple; very common along roadsides
and in dry rangelands in western North America; introduced from
Europe.

Centaurea jacea L., brown knapweed, centaurée jacée
Perennial; stems erect, 2 to 4 feet (6 to 12 dm.) high; flowers
rose-purple; locally common in pastures, and along roadsides in
southwestern Ontario, the Eastern Townships of Quebec, and in
the adjacent United States; introduced from Europe.

Centaurea maculosa Lam., spotted knapweed, centaurée maculée
Biennial or short-lived perennial; stems 2 to 6 feet (3 to 9
dm.) high; flowers purple, rarely white; locally common in
pastures and waste places in the east; common in the dry
rangelands of British Columbia, Washington, Oregon, Idaho, and
western Montana; introduced from Europe.

Erigeron philadelphicus L., Philadelphia fleabane, vergerette de Philadelphie
Perennial by stolons and offsets; stems 1 to 3 feet (3 to 9 dm.)
high; flowers usually a pale pink; throughout our range, but
less common in the mid-west and maritime areas; meadows,
pastures, swampy ground, woods, riverbanks, beaches, and
roadsides; native to North America.

Hypochaeris radicata L., spotted cat's-ear, porcelle enracinée
Perennial; stems 6 inches to 2 feet (15 cm. to 6 dm.) high;
flowers yellow; common only in the coastal areas of Oregon,
Washington, and southern British Columbia; pastures, waste
places, and along roadsides; introduced from Europe.Inula helenium L., elecampane, inule aunée
A coarse perennial herb, with rigid stems from 3 to 6 feet (9 to 18 dm.) high, that was introduced here from Eurasia as an ornamental and medicinal plant. It is an uncommon garden escape in fields, roadsides and waste places, especially near past or present habitations. It occurs in all areas except our Midwest.

Iva axillaris Pursh, povertyweed, ive à fleurs axillaires
Persistent-perennial, spreading by seeds and underground
rootstocks; stems 6 to 8 inches (15 to 20 cm.) high; flowers
inconspicuous, wind-pollinated; common in the prairie region,
less common in dry areas further west; native to the western
prairies of the United States and Canada. Where abundant, its
wind-blown pollen is an important cause of hay fever.

Iva xanthifolia Nutt., false ragweed, ive à feuilles de lampourde
Annual; stems 3 to 8 feet (9 to 24 dm.) high; flowers
inconspicuous, wind-pollinated; common in the mid-west, rare to
the east and west; cultivated land, waste land, and gardens;
native to North America. The abundant wind-blown pollen is an
important cause of hay fever. Contact with leaves produces a
dermatitis in some people. Milk from cows grazing this plant has
an undesirable flavor.

Lapsana communis L., nipplewort, lapsane commune
An annual or winter annual with stems 6 to 50 inches (15 to 125 cm) high. Flower heads are yellow, dandelion-like but much smaller at 3/8 to ¾ inch (1 to 2 cm) in diameter. Unlike dandelion, nipplewort has lyrate-lobed lower leaves and its seeds lack a parachute-like pappus. Nipplewort is a native of Europe and western Asia and was apparently introduced into our Continent in the 19th century. It now occurs in most of southern Canada and the northern United States. It is, however, rare or absent in much of the Midwest. Originally only a weed of gardens and waste places, it has now become an important weed of grain, forage and vegetable crops in some areas. It has the chromosome number of 2n= 14.Text and photos of nipplewort by Stephen J. Darbyshire.

Solidago canadensis L., Canada goldenrod, verge d’or du Canada.
Perennial, spreading by seeds and rootstocks; allogamous; stems
18 inches to 5 feet (45 cm. to 15 dm.) high; flowers yellow; in
the eastern half of our range; meadows, old fields, roadsides,
fencerows, and waste places; native of North America. Contrary
to popular belief, the goldenrods are not responsible for hay
fever. As a general rule, plants with showy flowers produce
relatively small amounts of pollen. Their pollen is sticky and
is programmed to adhere to insects and be transferred by them to
the stigmas of other flowers that they visit. It is the plants
with inconspicuous flowers, that produce large amounts of
lighter pollen that is blown indiscriminately by the wind, that
causes most hay fever in humans. This “wasteful” strategy
requires large amounts of pollen so that it can effectively come
in contact with the stigmas of other plants. Since the hay fever
season coincides with the simultaneous flowering of common
ragweed, with its inconspicuous flowers, and goldenrods, with
their conspicuous flowers, the wrong culprit often stands
accused.

Taraxacum officinale G.H.Weber ex Wiggers, dandelion, pissenlit officinal
Perennial, with a deep-penetrating tap root, spreading by seeds;
stems 3 inches to 1 foot (8 to 30 cm.) high; flowers yellow; one
of the most common weeds throughout our range; pastures, lawns,
waste places, hayfields, cultivated land, and roadsides;
introduced from Europe. Dandelion, like many plants of the
composite family, produces seeds attached to a feathery pappus.
The seeds attached to this “parachute” are disseminated widely
by the wind. In addition, our dandelion is a triploid that is
apomictic (does not require fertilization to produce seed).
These characteristics, plus a long tap root that can reach to a
considerable depth, makes dandelion a very successful colonizer
in many habitats over a wide area.Tragopogon dubius Scop. [ =Tragopogon major Jacq,],
goat's-beard, salsifis majeur
Biennial to perennial, spreading by seeds; autogamous; stems 6
inches to 2 feet (15 cm. to 6 dm.) high; flowers yellow;
throughout our range, but most common in the mid-west; pastures,
prairie, hayfields, waste places, and along roadsides;
introduced from Europe.

Tussilago farfara L., colt’s-foot, tussilage pas-d’âne
A perennial herb that spreads mainly by its extensive system of thick, white, horizontal, underground rhizomes. Bright yellow dandelion-like flowers appear in early spring well before the emergence of large heart-shaped leaves. Flowering stems are gray-wooly and 2 to 20 inches (5 to 50 cm.) tall. Colt’s-foot was introduced here from Europe and Asia for medicinal purposes. It should never be used internally because of its dangerous alkaloids. Colt’s-foot is locally common, in a wide range of habitats, in the eastern and extreme southwestern parts of Canada and in the eastern and northwestern United States. It can be an invasive plant, producing a dense canopy of leaves that will smother other vegetation.

Xanthium strumarium L., cocklebur, lampourde glouteron
Coarse annual herb; erect; 1 to 3 feet (3 to 9 dm) high; most common in moist ground, along shores, and in fields and waste places; widespread; both native and introduced populations occur in our area. Has poisoned cattle, sheep, and swine. Milk from cows grazing on its leaves has a very undesirable flavor. The fruit is bur-like. It often becomes entangled in the manes of farm animals, and it can also contaminate the wool of sheep.

Click on a photo to view an enlarged image.

Weed Name

Photo

Weed Name

Photo

common yarrow, achillée millefeuille(a large patch)

common yarrow, achillée millefeuille

common yarrow, achillée millefeuille(summer)

common yarrow, achillée millefeuille(winter)

Russian knapweed, centaurée de Russie(F&M)

Russian knapweed, centaurée de Russie

Russian knapweed, centaurée de Russie(flower, enlarged)

Russian knapweed, centaurée de Russie

white snakeroot, eupatoire rugueuse

white snakeroot, eupatoire rugueuse

common ragweed, petite herbe à poux

common ragweed, petite herbe à poux

common ragweed, petite herbe à poux

common ragweed, petite herbe à poux(many inflorescences)

common ragweed, petite herbe à poux(along edge of road)

common ragweed, petite herbe à poux(along edge of road)

common ragweed, petite herbe à poux(seedling, FF)

common ragweed, petite herbe à poux(NC)

common ragweed, petite herbe à poux (racemes of inconspicuous male flowers, close up; the source of wind-borne pollen that is one of the main causes of hay fever)